For example, JP-A-2003-98793 discloses an image forming apparatus, in which non-overlapping patterns, which do not include a part having a plurality of colors overlapped therein, are formed on both ends of a transfer belt in a belt width direction, optical sensors for reading the non-overlapping patterns are provided at both ends of the transfer belt in the belt width direction, and an adjustment processing of performing a color matching is executed based on reading results of the optical sensors.
Also, for example, JP-A-H06-1002 discloses an image forming apparatus, in which a transfer belt is formed with an overlapping pattern including a part having a plurality of colors overlapped therein, and an adjustment processing of performing a color matching is executed based on a reading result of an optical sensor for the overlapping pattern.